Some general updates, including initial 4.x updates

[deadbytefpv]

1. Notice about changing EdgeTX UI for colored-screen Radios.
2. Lua Script naming
3. Additional Baud Rate recommendations
4. New Lua Script options
5. Mentioning FlySky PA01
6. Linking Webflasher
7. ADC Filter setting for PWM receivers
8. Channel Mixing for PWM receivers
9. Moved BF Presets into Pre-First Flight page

I'll be making a separate PR for UI updates, unless someone has beat me to it.

[CapnBry]

Should we include the change to tx-prep to say the maximum baud for external modules is 3.75M now instead of 5.25M? It is just for F4 processors but I don't know if we need to start breaking it down by handset model AND external module model

EdgeTX/edgetx#6923

[deadbytefpv]

Should we include the change to tx-prep to say the maximum baud for external modules is 3.75M now instead of 5.25M? It is just for F4 processors but I don't know if we need to start breaking it down by handset model AND external module model

EdgeTX/edgetx#6923

I'll adjust accordingly.. Also have to rebase this after the previous Merge.

Thanks Cap'n.